The present invention relates to electron emissive electrodes used in electron discharge tubes and more particularly to an electrode with a very large area of electron emissive material.
Electron emissive electrodes are used in electron discharge tubes to emit a plurality of electrons in response to each impinging photon or photoelectron. Because of this property, electron multipliers are made utilizing these electrodes. The primary electrons can be photoelectrons from a photocathode or secondary electrons from another dynode. The problem that has been encountered in the construction of phototubes has been to collect efficiently electrons from one stage of an electron multiplier to another stage. In particular the problem has been to maximize the collection of electrons at the input stage of the electron multiplier, i.e., photoelectrons from a photocathode to the first dynode of an electron multiplier. An increase in the efficiency of collection of electrons at the input stage increases the signal-to-noise ratio. Thus, it is highly desirable to collect all the electrons that can be collected. For a photomultiplier tube this means the maximization of the collection of photoelectrons from the photocathode.
Cup shaped electron emissive electrodes are known in the art (see e.g. U.S. Pat. No. 3,849,644 issued to James Ibaugh on Nov. 19, 1974). However, that patent teaches the angular staggering of the cup shaped electrodes. This results in an electron discharge tube having a large axial dimension to accomodate the "staggered" electrodes.